Non-regular four blade shutter

ABSTRACT

A non-regular four-blade shutter for motion picture projector which provides a composite of a two-blade shutter which gives maximum light and a three-blade shutter which provides minimum flicker. The present shutter transmits more light than a threeblade shutter without undesirable light modulation or flicker.

United States Patent Yang Jan. 8, 1974 [54] NON-REGULAR FOUR BLADESHUTTER 2,073,798 3/1937 Hillman 352 208 [76] Inventor: Eugene Li-ChunYang, 710 W.

Haven Dr., Arlington Heights, Ill. primary Examiner Momoe Hayes 60095[22] Filed: Jan. 4, 1973 [21] Appl. No.: 320,870 ABSTRACT a Anon-regular four-blade shutter for motion picture [52] US. Cl. 352/208projector Which provides a composite f a twoblade [51] Int. Cl. G03b9/10 shutter Which gives maximum light and a three biade [58] Field ofSearch 352/208, 219, 220 Shutter which provides minimum flicker. Thepresent shutter transmits more light than a three-blade shutter [56]References C'ted without undesirable light modulation or flicker.

UNITED STATES PATENTS 7 2,052,960 9/1936 Berggren 352/208 2 Claims, 2Drawing Figures NON-REGULAR FOUR BLADE SHUTTER This invention relates toshutters for motion picture projectors, and more particularly, to anon-regular four-blade shutter.

ln motion picture projectors, two-blade shutters transmit maximum lightand three-blade shutters provide minimum flicker. Various attempts havebeen made to get more light transmission from a three-blade shutter bymaking it asymmetric. However, this results in undesirable lightmodulation' The present invention provides a shutter whereby light isincreased over a three-blade shutter without undesirable side effects..The present invention cancontinuously bridge the gap between atwo-blade and a three-blade shutter. For instance, it can provide ashutter having light transmission equivalent to a 2.5-blade shutterwithout undesirable side effects.

A typical three-blade shutter has blades with an included angle of 50which would give 210 of light exposure. The shutter of the presentinvention will give more light exposure than this without undesirableside effects such as light modulation and flicker, which are annoying tothe viewer. The providing of more light lowers the power requirementsfor the projector.

Accordingly, a principal object of the invention is to provide new andimproved shutter means for motion picture projectors.

Another object of the invention is to provide a new and improvedfour-blade shutter for a motion picture projector.

Another object of the invention is to provide a new and improved shutterfor motion picture projectors which transmit more light than aconventional threeblade shutter without undesirable light modulation orflicker.

Another object of the invention is to provide a new and improvedfour-blade shutter having light transmissioncharacteristic between thatof a twoblade shutter and that of a three-blade shutter.

These and other objects of the invention will be apparent from thefollowing specification and drawings, of which:

FIG. 1 is a plan view of an embodiment of the invention.

FIG. 2 is a plan view of an embodiment of the invention havingequivalent light trnasmission of a 2.5-blade shutter.

FIG. 1 is a generalized configuration of the invention.

Blades 1b and blade 4 are diametrically opposite and 60 each measures adegrees. Thus the composite shutter is a superposition of a three-bladeshutter with a two 5 generates into a regular two-blade shutter. lf 0 aC l0 erned by the pulldown angle of the film-indexing mechanism. One isfree to choose a to obtain the desired light output. After choosing a,the other angles are given by the following equations:

S=C-a d=one-half (a) More specifically, referring to FIG. 1, theinvention is a composite of a three-blade shutter having blades la, 2and 3 each having an included angle of 8, and a shutter comprising ofblades lb and 4 each having an included angle of a and are diameticallyopposite of each other. Blades la and 1b merge to form blade 1 whichtogether with blades 2,4, and 3 constitutes a non- 25 regular four-bladeshutter. The angle a may be chosen by experimentation for a particularapplication, and the other angles will be given by the equations listedabove. The angle C is a constant which is equal to the pulldownmechanism of the film advance, i.e., the angle of 0 the film cyclewherein thefllm is being advanced.

Referring to FIG. 2, a specific example is given for C=50. Ifa is chosento be 25, then S=25, and the specific measurements are as shown.

Having 235 of exposure, this shutter is equivalent to 35 a shutterhaving 2.5 50-blades in terms of light output (for C=50, a two-bladeshutter has 260 of exposure while a three-blade shutter has a 210 ofexposure). This shutter gives greater light output than a threebladeshutter, yet exhibits, subjectively, less temporal 40 light modulationthan a two-blade shutter.

I claim:

1. A four-blade shutter for a motion picture projector wherein C is thepulldown angle of the film-advance mechanism of said projectorcomprising:

a first blade having an included angle of C degrees which is visualizedto consist of two joined parts la and lb measuring respectively Sdegrees and a degrees, blade la being symmetric about line L1,

second and third blades, each'measuring S degrees and symmetricallylocated about lines L2 and L3 where L1, L2 and L3 are spaced l20 apart,and

a fourth blade diametrically opposite 1b measuring a degrees. 2.Apparatus as in claim 1 and having the following 5 parameters:

S C (N, 2)

d C (one-half) (3-N where N, is the equivalent number of blades and 2 5N s 3, and d is the angle between a line L, bisecting said first bladeand a line L1 bisecting part 1a of said first blade.

1. A four-blade shutter for a motion picture projector wherein C* is thepulldown angle of the film-advance mechanism of said projectorcomprising: a first blade having an included angle of C degrees which isvisualized to consist of two joined parts 1a and 1b measuringrespectively S degrees and a degrees, blade 1a being symmetric aboutline L1, second and third blades, each measuring S degrees andsymmetrically located about lines L2 and L3 where L1, L2 and L3 arespaced 120* apart, and a fourth blade diametrically opposite 1bmeasuring a degrees.
 2. Apparatus as in claim 1 and having the followingparameters: a C (3-Ne) S C (N3 - 2) d C (one-half) (3-Ne) where Ne isthe equivalent number of blades and 2 < or = Ne < or = 3, and d is theangle between a line Lv bisecting said first blade and a line L1bisecting part 1a of said first blade.